1. Field of the Invention
The present invention relates to a method for transmitting data in a hub-based local area network (LAN), and more particularly to a data transmission method suitable for improving the transmission performance of the LAN as a whole in a simple method.
2. Description of the Related Art
In order to improve the transmission performance of the network, there has so far been a hub-based network directly accommodating a plurality of local area network communication devices in a hub through transmission lines. A hub-based network using a hub called a multiport bridge or a multiport router is reported in, for example, "Bridges and Routers", IEEE Network, Vol. 2, No. 1, January, 1988, pp. 57-64, by William M. Seifert.
Usually, a bridge or a router is used to connect between LANs to enable each LAN to independently transmit packet information, unlike repeaters that have only a signal relaying function. By referring to a destination address of packet information that has been received by a bridge or a router, a LAN decides whether this information should be discarded or retransmitted (a filtering function). In the latter case, that is, when the destination address is not the address of a communication device connected to the LAN of a receiving port, the packet information is retransmitted to another port which requires this information (a forwarding function). As compared with a single LAN system, this method enables a traffic to be limited to a necessary place to thereby increase the traffic volume of the system as a whole, as described above.
As is clear from the above explanation, it can be considered that packet information is burst-switched in a multiport bridge or router that enables a mutual connection between a large number of LANs.
There are examples of a network for integratingly switching both packet information and isochronous information, as described in "An Integrated PBX/LAN System Architecture", IEEE ICC, June, 1988, pp. 1533-1538, by Eiichi Amada, et al. and "IVD-LAN Having Reached a Stage of Practical Development" (in Japanese), Computer & Network LAN, September, 1990, pp. 11-16, by Shimizu.
In the above-described example, a communication device of a local area network such as an Ethernet is converted into an IEEE802.9 IVD-LAN (Integrated Voice & Data LAN) interface by a terminal adaptor and is accommodated in a central switching unit, where the packet information is switched by a burst switching unit and the line information is switched by a Private Branch Exchange (PBX) unit.
According to the above-described conventional technique, there have been problems that, when a communication device of each local area network has transmitted packet information, it is not possible to directly confirm whether or not the packet information transmitted has reached another communication device that should receive the packet information, and a loss of packet information could easily occur when the information is switched integrally.
Further, according to the conventional technique, packet information is stored in the hub. The hub receives packet information on behalf of the communication device which should receive the information and stores the packet information in the buffer memory thereof as long as there is room in the buffer memory at the forwarding time. Therefore, there has also been a problem that there is a large time variation in the period from when the packet information is transmitted till when it reaches the communication device that should receive the information, taking much time in retransmitting the received package information.